This invention relates to nuclear reactors, and more particularly to the improvement of a nuclear reactor of the type which is provided with internal pumps for forcing a coolant to circulate within the reactor through a reactor core.
The aforesaid type of nuclear reactor comprises a shroud enclosing the reactor core, and a pressure vessel surrounding the shroud, with a vertical annular space being defined between the shroud and the pressure vessel. Installed in a lower portion of the vertical annular space are a plurality of internal circulation pumps for forcing a coolant in the vertical annular space to flow into below the reactor core so that the collant flows through the reactor core in forced circulation.
One of the problems encountered with regard to the aforesaid type of reactor is that the flow conditions of the coolant flowing through the reactor core tend to become unstable. For example, if the flow of the coolant in the reactor core is influenced by some disturbance, the flow rate of the coolant will tend to fluctuate, and once fluctuation of the flow rate occurs the flow rate repeatedly increases and decreases before stable flow conditions are restored after a prolonged period of fluctuation.
Reactors belonging to the aforesaid type include those of different constructional arrangements, and in some of them difficulties have been experienced in obtaining measurements of the flow rate of a coolant flowing through the reactor core due to the positional relation of equipment arranged in the pressure vessel and elsewhere.